Limited environmental water entitlement during summer/autumn 2018/19 prevented delivery of recommended flows for the mid and lower MacKenzie River and upper Burnt Creek. Previously, this scenario resulted in ‘system resets’ where refuge pools were presumed to have dried out and aquatic fauna lost (e.g. 2012/13 and 2014/15). Environmental watering in 2016/17 and 2017/18 re-established important fish and crayfish populations.
Ecology Australia worked with the Wimmera Catchment Management Authority to identify key refuge pools, rapidly collect baseline fish and crayfish data, workshop optimal autumn/summer environmental watering regimes based on limited water availability, and to establish minimum depth thresholds and depth monitoring regime for refuge pools. This was followed by post-implementation rapid surveys to assess population persistence in years where the watering regime was implemented (2020, 2022) and post significant flooding events (2023).
The environmental watering regime prioritised conserving refuge pools through periodic low flows, followed by provision of winter/spring releases for obscure galaxias spawning when enough water is available. This took precedence over summer and autumn ‘freshes’ previously considered a high priority. Self-sustaining populations of important fish and crayfish persisted at all refuge sites in 2019 and subsequent monitoring years. Realistic potential now exists for some of these species to recolonise the Wimmera River and for river blackfish to be reintroduced to Burnt Creek, where a population existed until 2002.
Fluctuating environmental entitlement volumes often prevent the full range of recommended watering actions. When water availability is limited, maintaining refuges is critical for the persistence of aquatic values.